A vibration felt through the center floor of the vehicle can be caused by cracked and/or shredded driveshaft flex discs, resulting in excessive driveshaft movement. If not repaired, damage to the driveshaft center support bearing, transmission, or differential can occur.Google+
Car Problem Reports
Mercedes-Benz CLK320 Cracked Driveshaft Flex Discs May Cause Driveshaft Movement/Vibration
Mercedes-Benz CLK320 Problem
Average Mileage: 136,500 mi (75,000 mi - 198,000 mi)
I have had the same issue since I had my MB CLK 320 year 2000. There has been a vibration. I changed A lot on the car to the check engine light went out, even motor mounts. Now it feels like there is something rattling right under the driver side by the exhaust and converter. And the vibration is crazy.